The present invention relates to optic mounts, particularly to optical mounts having means for adjustment about X, Y and Z axes, and more particularly to an actuator that can precisely actuate three degrees of freedom of a suspended component, such as an optic mount, commonly referred to as tip, tilt, and piston, while also providing exact constraint.
Optics for use in imaging system, such as extreme ultraviolet lithography (EUVL), require reflective optics that are precisely figured to the Angstrom level. This requirement is expanding the state of the art in optics manufacturing and in opto-mechanical system design. There is a need in the art to position precisely and remotely the optical surface in three degrees of freedom, commonly referred to as tip, tilt, and piston. Quite often these degrees of freedom are provided serially as two independent rotations about X and Y axes and an independent translation along the Z axis, which is perpendicular to the optical surface. However, for the precision required by imaging systems, such as EUVL, it is difficult or perhaps impossible to obtain sufficient rigidity and dimensional stability in a serial mechanism.
The present invention addresses the particular challenge to position precisely and remotely the optical surface in tip, tilt and piston (three degrees of freedom). The invention belongs to the class of parallel-link mechanisms, which offer significant advantages at the complication of coordinated axis moves, which is not at all significant for tip, tilt and piston. Besides being stiffer, parallel-link mechanisms provide exact constraint for the suspended element (optical surface). This is important for an optic mount since over-constraint can negatively influence the figure of the optic.
The precise motions and long term dimensional stability required for EUVL naturally favor the use of blade flexures, rather than ball joints and hinges, which function as simple hinge joints but without friction and backlash. Frequently, flexure mechanisms are designed to provide mechanical advantage for more precise actuation. This invention incorporates mechanical advantage into each flexure mechanism with one extra hinge axis. Basically, the precision tip-tilt-piston actuator of this invention consists of three flexure mechanisms, an optic mount to be supported and positioned, a structure that supports the flexure mechanisms, and three commercially available linear actuators. Blade flexures are used as simple hinge joints in the flexure mechanisms because they operate without friction and backlash.